This invention relates to a flat-panel display device having a backlight and, more particularly, to a liquid-crystal display device having an electromagnetic shielding sheet or plate disposed around a lamp of the backlight.
Recently, flat-panel display devices such as liquid-crystal display devices have been used as image display devices for wide range of computers and mobile information appliances, car navigation system and the like because of their features that they are thin and light-weighted and consume a small electric power. Particularly, the flat-panel display devices has come to be widely used for television setsxe2x80x94ranging from small mobile one to on-wall placing large one, for a car navigation system and the like, and for various computers, car navigation systems and the like.
Heretofore, a light-transmissive liquid-crystal display device for displaying a high-definition image is exemplified.
The liquid-crystal display device is comprised of, at least, a liquid-crystal panel formed of a pair of transparent substrate plate with a liquid crystal sandwiched therebetween; a surface illuminant device, referred as a backlight, disposed along rear face of the liquid-crystal panel and supplying a light from light source to the rear face; and a shield casing in a picture-frame shape, referred as a bezel cover, which covers all periphery and its vicinity, of the liquid-crystal display device in a manner for reducing an electromagnetic noise and a manner for enhancing mechanical strength of the liquid-crystal display device.
In the above, a lamp in the surface illuminant device is usually a luminescence lamp driven by a high-frequency electricity and thus becomes an electromagnetic noise source. When the liquid-crystal display undergoes an effect of the electromagnetic noise, a stripe pattern may appear on the displaying screen to impair discernability or display quality on the displaying screen. In view of this, JP-A-05324175 (JP-A-1993-324175, Japanese unexamined patent publication No.5-324175(1993)) discloses a construction of the liquid-crystal display in which the electromagnetic noise emitted from the surface illuminant device is prevented from affecting the liquid-crystal panel. The disclosed construction is hereunder explained by referring to a cross sectional view of the liquid-crystal panel shown in FIG. 4. A surface of a lamp holder 31 for a luminescence lamp disposed along a periphery of the liquid-crystal panel is electroplated with nickel or copper to effect grounding of the lamp holder 31. A general construction for the grounding is such that a shielding sheet or a lamp cover formed of electro-conductive material is disposed in a vicinity of the luminescence lamp in the surface illuminant device and is connected with the shield casing to effect the grounding.
A detailed construction for the grounding in prior art is disclosed in JP-A-10096947 (JP-A-1998-096947, Japanese unexamined patent publication No.10 96947(1998)), and is shown in FIG. 5. As shown in FIG. 5, a lip 35 extended from the shield casing 33 is electrically connected with a lamp cover 34 by soldering. Although such construction enables strong and rigid adhering, very strong mechanical shock may peel off the solder. Moreover, such construction requires cost increase because the lip 35 and the shield casing 33 have to be formed of copper, which is relatively expensive and is needed for enabling the soldering.
Whereas, in hereabove, electromagnetic shielding constructions using a lamp cover are explained, FIG. 6 shows a typical construction using a shielding sheet such as an aluminum foil, where the shielding sheet is connected with the shield casing by soldering. A surface illuminant device shown in the FIG. 6 is of sidelight type or edge-light type. The surface illuminant device comprises; a resin frame 21 on which a liquid-crystal panel 4 is placed; a light-guide plate 22 accommodated inside of the resin frame 21; optical films 23 placed on the light-guide plate 22; and a tubular light source 24 disposed along an edge of the light-guide plate 22. A shield sheet 2 is disposed inside of the resin frame 21 so as to cover at least back surface of the light-guide plate 22 and backside of the tubular light source 24.
A portion of the shield sheet 2 is pulled out from the inside of the resin frame 21 and is connected with a shield casing 3 by soldering to effect grounding of the shield sheet 2 at the time the shield casing 3 is assembled with the resin frame 21. Due to use of soldering in this prior art, above-mentioned problem should also be arisen.
Another construction in the prior art is shown in FIG. 7. For basic construction is same with that shown in the FIG. 6, explanation of them will be omitted. In a construction shown in the FIG. 7, a first resin frame 21 and a second resin frame 25 are assembled to be fastened together by a latching pawl 25a projected from the second resin frame 25. A portion of the shield sheet 2 is pulled out from inside of the resin frames 21,25 to form a pulled-out portion 2a on inner surface of the shield casing 3 and to cover the latching pawl 2a. In this way, grounding of the shield sheet 2 is achieved by directly contacting the shield sheet 2 with the shield casing 3. However, this construction has a following drawbackxe2x80x94electric connection of the shield sheet 2 with the shield casing 3 should be momentarily disconnected to momentarily disrupt grounding when the shield casing 3 undergoes a momentary deformation incurred by a mechanical shock or the like. Thus, a noise pattern may appear momentarily on the display screen.
As explained above, prior art techniques for grounding the shield sheet by connecting with the shield casing give rise drawbacks: Use of soldering for connecting requires use of expensive material such as copper and may incur disconnecting of the connection. Meanwhile, a shield casing is constructed to sandwichedly press the portion of the shield sheet on the resin frame for effecting the connection for the grounding; thus, the connection for the grounding is unreliable under a mechanical shock.
In view of the above drawbacks, the present invention is aimed to provide a flat-panel display which has enhanced reliability in the connection for grounding the shielding flat conductor such as a shield sheet even under a condition mechanical shocks are incurred as in a car navigation system, and which is capable to keep assembling cost to be low enough.
To achieve the aim, an invention-wise flat-panel display comprising: a light-guide plate; a tubular light source disposed at least along one edge of the light-guide plate; a flat conductor disposed along at least part of a main face of the light-guide plate and along at least a region that covers circumferential surface of the tubular light source except with a light-guide-plate side of the tubular light source; a frame accommodating, at least, the light-guide plate, the tubular light source and the flat conductor; a display panel being placed above another main face of the light-guide plate; an electrically-conductive casing that hold the display panel so as to be sandwiched between the frame and the electrically-conductive casing; an electrically-connecting conductor element having a first leaf spring pressed and sandwiched between the flat conductor and the frame and a second leaf spring pressed and sandwiched between the electrically-conductive casing and the frame.
In another aspect of the present invention, a flat-panel display device comprising: a frame having a base plate, sidewalls extending upward from a whole periphery of the base plate, a slit on one of the side walls disposed at a position to join the base plate and a recess on an upper face of the base plate that extends inward from the slit; a flat conductor disposed at least on part of the upper face of the base plate and to contact an inner face of said one of side walls, said flat conductor being folded to be substantially C-shaped in a vicinity of said one of side walls at a cross sectional view; a light-guide plate placed on said upper face of the base plate through the flat conductor therebetween; a tubular light source disposed between said one of sidewalls and the light-guide plate, a circumferential surface of said tubular light source being disposed in a vicinity of the flat conductor except with a light-guide-plate side of the circumferential surface; a display panel being placed above the light-guide plate; an electrically-connecting conductor element having a first leaf spring pressed and sandwiched between the flat conductor and the frame as being inserted from the slit and a second leaf spring contacting on an outer face of said one of side walls; and an electrically-conductive casing that hold the second leaf spring so as to be sandwiched between said one of sidewalls and the electrically-conductive casing.
By this feature, enhanced reliability in the connection for grounding the flat conductor is achieved while keeping the assembling cost to be low enough.